Ladders have become a useful tool to almost every individual in society and permit individuals to climb to heights unreachable by the unaided. Individual ladders can range from small stepladders having 2-3 rungs allowing an individual to access that one item just out of reach to large extension ladders that can extend to 40 feet and more for scaling large walls, trees, and buildings. One or more ladders can be found in almost every household and are utilized by professional tradesmen of all types.
Unfortunately, the design and usage of a ladder also contributes to its inherent instability and danger. A ladder is typically constructed of two spaced apart vertical stiles with a plurality of regularly spaced rungs extending between the stiles. The bottom end of each stile also functions as the support foot for the ladder at its base. While the base of some ladders may be wider than the ladder top, the overall width of the ladder is relatively narrow when compared to its height. As the width to height ratio decreases (with increasing ladder height) the lateral stability of the ladder also decreases such that a minor lateral shift in the combined center of gravity of the ladder, including the user who is climbing the ladder, can result in an unwanted lateral shift of the ladder. As the user climbs the ladder the combined center of gravity also translates up the ladder, and consequently the danger from a minor lateral shift in the center of gravity increases proportionately as the center of gravity rises. In extreme cases, the unwanted lateral shift can and often does result in the ladder falling to the ground with the user suffering serious injuries as a result thereof. The U.S. Consumer Product Safety Commission (CPSC) reports that each year there are in excess of 150,000 emergency room-treated injuries in the U.S. relating to ladders. A significant portion of which are attributable to ladder falls.
These instabilities require the total concentration of the individual climbing or descending the ladder. Probably the greatest danger to a climber is when he is approaching the topmost or bottommost rungs. He is often unable to look down to determine on which rung he is standing. Consequently, while ascending, he may think he has more rungs on which he can step at the top of the ladder thereby resulting in the ladder tipping or losing a stable foothold resulting in the ladder tipping while at a significant height. Also, when descending, he may believe he is on the bottom rung and prepare his next step for dismounting from the ladder. If however, he has misjudged the rung, he may end up attempting to dismount from a rung higher on the ladder and then fall the remainder of the way to the ground.
The inability to determine the exact rung on which he is standing at the top while climbing or at the bottom when descending will very likely result in injury to the climber unless he is able to determine when he has reached a specific top or bottom rung. Therefore, there is a need for a warning system on the ladder to automatically indicate to the climber when he has reached the top or the bottom to prevent injury to the climber.